I'm a Realtor.
According to the National Association of Realtors about 1/2 of licensed agents are not full-time so absolutely it's something that many people are doing.
The barrier to entry to become a license agent is pretty low. In Minnesota you pay around $1k for 90 hours of classroom training and taking the test. Classroom can be done days, nights or weekends.
You then find a broker to take your salesperson license so you can practice. As a part-time agent you'd probably want to find a broker that is friendly to new agents and has a commission model that takes less in fees in exchange for more of the cut out of every closed transaction.
The biggest thing to keep in mind is that you probably need to sell 2-3 deals a year just to break even. You have ongoing costs associated every year that include - MLS access, Realtor Association Dues, Errors & Omissions Insurance, Continuing Education. Figure $1-2k for all of those. Depending on the broker you choose you could have other costs as well - for example, I pay $400 a year to be a RE/MAX agent that goes to corporate.
Then you have your costs of doing business - marketing materials, car expenses, costs with actually listing a home (buying signs, sign installation, photography, staging, brochures), copying/printing (most brokers charge you for every page) and finally the cost of being an independent contractor like paying both sides of FICA.
During the mid-2000's there were 22,000 licensed agents in the Twin Cities as houses were flying off the market and it was easy pickings. By 2009 it was down to 15,000 agents as sales volume fell in the tank and all of those people who got into the market for the easy sales found out that the costs of maintaining their license just weren't worth it.
The other question you should ask is whether you have a circle of people that will use you and trust you enough to handle the largest financial transaction they have? There's also a risk that serving family and friends can cause issues if their transaction doesn't go smoothly. How will you feel when friends don't select you? How will you handle expectations of discounted services as a family member or friend?
Hope that helps